1. Field of the Invention
This invention relates to an exhaust system for an internal combustion engine and, more particularly, to an exhaust system having a conduit for transferring exhaust gases from the engine, as well as a port disposed along the conduit for admitting secondary air into the conduit to draw exhaust gases from the combustion chamber and to increase combustion of the exhaust gases.
2. Description of the Prior Art
Internal combustion engines produce emissions of exhaust gases, such as carbon monoxide, hydrocarbons and nitrogen oxides, that contribute to atmospheric pollution. The level of pollution is typically higher, oftentimes well beyond levels considered acceptable by federal and state emission guidelines, when the fuel burned by the engine is not fully combusted, i.e., in cases of incomplete combustion.
Various methods have been attempted to reduce the amount of polluting exhaust gases emanating from internal combustion engines. For example, as disclosed in U.S. Pat. No. 4,240,254, catalytic converters have been installed in exhaust systems to oxidize exhaust gases thereby reducing pollution. While generally effective in reducing pollution, catalytic converters have several disadvantages, including high cost, unreliability, warm-up time, creation of by-products, and reduction in power and efficiency of the engine.
Alternatively, as disclosed in U.S. Pat. Nos. 3,662,541 and 4,133,175, air may be combined with the exhaust gases leaving the combustion chamber to improve combustion and oxidation of exhaust gases while in the exhaust manifold. In the conventional exhaust systems, the additional air is mixed with the exhaust gases immediately adjacent the exhaust port of the cylinder head or within the cylinder block, and often in a direction opposite to the flow of the exhaust gases. A significant drawback to this arrangement is that a certain level of back pressure occurs as a result of mixing the additional air and the exhaust gases proximate the exhaust chamber, particularly if the air is directed against the flow of exhaust gases. The back pressure increases the force required for the pistons to push the exhaust gases out of the combustion chambers causing a corresponding reduction in the power and efficiency of the engine.
In addition, in conventional exhaust systems, such as those disclosed in U.S. Pat. Nos. 3,662,541, 4,133,175, and 4,240,254, the individual exhaust pipes from each exhaust chamber merge substantially close to the engine block into one or two common exhaust pipes that lead to a muffler and tailpipe assembly. The conventional systems do not take into consideration the temperature in the exhaust pipes in determining where to merge the exhaust pipes. As a consequence, the portion of exhaust not fully burned in the combustion chamber has less opportunity to burn in the individual exhaust pipes where the temperature is highest and the most efficient combustion occurs. Moreover, when the exhaust pipes merge, the exhaust gases create additional back pressure resulting from interference between the various pulses of exhaust gases exiting the individual exhaust pipes. The back pressure reduces the power and operational efficiency of the engine, while the interference inhibits combustion.